The trial of Mauritanian opposition leader Mohammed Khouna Ould Haidallah on charges of plotting to stage a coup has begun in Mauritania's capital, Nouakchott.

Thousands of Mr. Haidallah's supporters turned up outside the criminal court buildings Monday in a show of solidarity.

Among them was Boubacar Ould Messaoud, the president of SOS Slaves, Mauritania's largest human rights group. SOS Slaves is outlawed by the government and Mr. Messaoud has been imprisoned for speaking out against the government on numerous occasions.

Crowds gathered around Mr. Messaoud and cheered as he said Mauritanians have the right to justice and proper defense.

Last week, lawyers defending Mr. Haidallah and 14 others from his group said they feared their clients would not get a fair trial. Since his arrest last month, Mr. Haidallah has not had access to his lawyers, his family or medical treatment.

Government security forces say they have evidence that Mr. Haidallah, a former military leader of Mauritania, was plotting a coup around the time of the presidential election on November 7. They said they found guns in his house and that he had received funds from Libya to finance the plot.

Libya has strongly denied any involvement in an anti-government plot in Mauritania.

President Maaouiya Ould Taya, who also came to power through a coup, was returned to office with 67 percent of the vote. The elections themselves were clouded by accusations of vote rigging and irregularities.

Opposition to Mr. Taya's near 20-year rule is growing, and human rights activists warn of a backlash against his government. Mr. Taya narrowly survived an attempted coup in June.